Abstract
Abstract. In a sensitivity experiment, an eddy-permitting ocean general circulation model is forced with realistic freshwater fluxes from the Greenland Ice Sheet, averaged for the period 1991–2000. The fluxes are obtained with a mass balance model for the ice sheet, forced with the ERA-40 reanalysis dataset. The freshwater flux is distributed around Greenland as an additional term in prescribed runoff, representing seasonal melting of the ice sheet and a fixed year-round iceberg calving flux, for 8.5 model years. By adding Greenland freshwater fluxes with realistic geographical distribution and seasonality, the experiment is designed to investigate the oceanic response to a sudden and spatially/temporally uniform amplification of ice sheet melting and discharge, rather than localized or gradual changes in freshwater flux. The impacts on regional hydrography and circulation are investigated by comparing the sensitivity experiment to a control experiment, without additional fluxes. By the end of the sensitivity experiment, the majority of additional fresh water has accumulated in Baffin Bay, and only a small fraction has reached the interior of the Labrador Sea, where winter mixed layer depth is sensitive to small changes in salinity. As a consequence, the impact on large-scale circulation is very slight. An indirect impact of strong freshening off the west coast of Greenland is a small anti-cyclonic component to the circulation around Greenland, which opposes the wind-driven cyclonic circulation and reduces net southward flow through the Canadian Archipelago by ~10%. Implications for the post-2000 acceleration of Greenland mass loss are discussed.
Highlights
The Greenland Ice Sheet (GrIS) appears to have been losing mass since the 1990s (van den Broeke et al, 2009)
By the end of the sensitivity experiment, the majority of additional fresh water has accumulated in Baffin Bay, and only a small fraction has reached the interior of the Labrador Sea, where winter mixed layer depth is sensitive to small changes in salinity
An anomalous fresh signal can be traced along the narrow boundary current of the Labrador Sea, relatively little additional freshwater reaches the interior of the subpolar gyre, where only small negative anomalies develop by 2001
Summary
The Greenland Ice Sheet (GrIS) appears to have been losing mass since the 1990s (van den Broeke et al, 2009). These data can be combined with estimates of grounding line fluxes from satellite observations of velocity (Rignot and Kanagaratnam, 2006) to produce the spatial distribution of freshwater fluxes (FWF), which can be prescribed as forcing in an ocean circulation model. Such an experiment has been undertaken using rough estimates of FWF from Greenland and Antarctica in a global model with 1◦ resolution (Stammer, 2008). Caveats inherent in the present experimental design are considered
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